Method of controlling sand



Oct. 11, 1966 F10. BOHN 3,277,961

METHOD OF CONTROLLING SAND Filed Aug. 19, 1963 INVENTOR. FIG. I FLOYD o. BQHN ATTORNEY United States Patent M 3,277,961 METHOD OF CONTROLLING SAND Floyd 0. Bohn, Houston, T ex., assignor to Dresser Industries, Inc., Dallas, Tex., a corporation of Delaware Filed Aug. 19, 1963, Ser. No. 303,103 4 Claims. (Cl. 166-5) This is a continuation-in-part of application Ser. No. 240,063, filed Nov. 26, 1962, now abandoned.

This invention relates to the completion of wells and more particularly to a method of controlling sand in the completion of a well in an unconsolidated formation.

In order to obtain oil, gas or water from a potential producing zone, a well bore is drilled into the producing zone. It is customary to line the well bore with a steel casing adjacent the potential producing zone and completely fill the space between the outside of the casing and the formation with a cement sheath or annulus. To get the oil or gas into the casing and consequently to the surface, it is necessary to perforate the casing and the cement sheath thereby permitting the fluid in the formation to flow into the casing. Perforating is usually performed by lowering a specially constructed gun into the casing, positioning it adjacent the proper zone and then firing it. The shot (either bullet or jet) penetrates the casing, cement sheath and enters the formation thereby forming a passage through which fluid in the formation can flow into the casing. If the potential producing zone is limestone, or consolidated sandstone, there is no particular problem except to obtain the greatest penetration possible. However, if the potential producing zone is an unconsolidated formation or a sand of low compressive strength, there is the probability of sand co-mingling with the fluid and flowing into the well casing. If the pressure in the formation is fairly high, the sand will flow, comingled with the fluid, to the surface where, by its very nature, it will cause trouble by cutting chokes, valves, filling tanks, etc. If the pressure is not too great the sand will have a tendency to settle out, compacting and sanding up the casing, preventing further flow. Various steps have been taken by the industry to minimize the sand problem in unconsolidated formations. Some of these steps have been preslotting the section of casing which will be adjacent the producing zone, the use of gravel packing as a filter, the use of screens, and the attempted consolidation of the formation by plastics or other binders. One other method has been to use small diameter bullets fired either singly or in a group. Although slotting, gravel packs, screens and consolidation techniques have had success ratios as high as 70 to 80%, they are expensive and, in some instances, may be more expensive than the potential amount of recovery from a marginal zone. Prior to the present invention, the use of small diameter bullets, singly or in groups, was not successful in holding back unconsolidated formations because of the hole size in the casing and the lack of atten tion to the cement sheath and the pattern of perforation. Long experience in the perforation of casings has shown it is practically impossible to obtain adequate penetration with bullets having a diameter of or less. Therefore, it was found impractical to perforate casing with a hole sufficiently small to cause bridging of sand grains of the size commonly found in production reservoirs, where the sand grains may be in the order of .002 to .020 in diameter. However, it was found that by utilizing the well perforating apparatus, fully described in my copending application S.N. 240,063, filed Nov. 26, 1962, now abandoned, of which this application is a continuation in part, and by practicing the method hereinafter set forth that sand could be controlled in unconsolidated formations in an effective manner at an economical cost.

3,277,961 Patented Oct. 11, 1966 It is an object of the present invention to provide a method of completing an unconsolidated zone in a manner which will provide effective sand control.

It is another object to provide an efficient, effective, economical sand control method for the completion of unconsolidated zones.

It is still another object to provide an effective method of sand control for unconsolidated zones which requires no special preparation of the casing, formations or the inclusion of extraneous items, such as screens.

It is a further object to provide an effective method of sand control in an unconsolidated formation by using an array of small diameter bullets for perforating the casing.

It is still a further object to provide an effective method of sand control in the completion of an unconsolidated formation by establishing that there is a complete hard, well set cement sheath at the zone to be perforated and then perforating the casing and cement annulus with an array of small diameter bullets which fracture the cement sheath forming bridging conditions for the sand.

The above objects are achieved by forming a complete sheath of neat cement between the outside wall of the casing and the wall of the well bore. The cement sheath is allowed to fully set and harden. The well is then logged to establish that there is a complete cement sheath in the potential zone of interest. The casing and sheath are then perforated with an array of small diameter bullets which penetrate the casing, sheath and extend into the formation. It has been found that the perforations cause the well set hard cement sheath to fracture, with the fragmented portions of the sheath tending to close the perforations, thereby forming small fissures which permit the unconsolidated sand in the formation to form bridges and not enter the casing. At the same time, the fluid in the formation can flow through the various fissures into the casing and thence to the surface.

The novel features of the present invention are set forth in particularity in the appended claims. The present invention, both as to its organization and manner of operation, together with other objects and advantages thereof, may best be understood by way of illustration and example of certain embodiments when taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a cross sectional view of a portion of a zone of unconsolidated formation, after the perforation of the casing and sheath.

FIGURE 2 is an elevational view of a portion of a perforating gun which may be used in carrying out the method.

FIGURE 3 is a cross sectional view taken generally along line 33 of FIGURE 2.

Referring now to FIGURE 1, there is shown a well bore 10 which extends into an unconsolidated formation 12, which appears from logs to be a potential producing zone. The well bore 10 is provided with a casing or tubing 14, at least adjacent the potential producing zone.

Since drilling of the well bore 10 does not result in a straight smooth cavity in which casing 14 can be located in seal tight relationship with the wall of the formation, it is common practice in the industry to form a cement sheath or annulus 16 about the casing 14 and in contact with the formation 12. One aspect of this invention requires that the cement sheath 16 be formed of friable cement, that is, regular well cement without any additives for the purpose of softening or reducing friability. The cement sheath 16 is allowed to set and completely harden. It is also essential that there be a good bond between the casing 14 and the cement sheath 16. After the sheath 16 has set and hardened, the well 10 is logged to ascertain the condition of the cement sheath 16 in the zone of interest. It has been found that in order to successfully practice the invention, the space between the casing and the formation must be completely filled with hard cement in the zone of interest and that there must be a good bond between the casing 14 and cement sheath 16. Therefore, .it is very desirable to make a cement bond long of the formation, particularly in the zone of interest to establish the condition of the cement sheath 16 at this location. The well bore is now in condition for perforation. The requirements above stated, do not require the use of extraneous materials or plasticizing the formation itself as was required by previous methods of sand control.

The perforating of the casing 14 and sheath 16 may M accomplished by the use of a bullet perforating gun 20 shown in detail in FIGS. 2 and 3 which is lowered into the well bore by a cable (not shown) and located opposite the zone of interest, see FIG. 1. This gun is similar to the one fully disclosed in my previously mentioned copending application, S. N. 240,063. As can be seen in FIG. 2, instead of having a single bullet, as is customary in bullet perforating guns, the perforating gun 20 has an array of bullets 22.

Turning now to FIGS. 2 and 3, there is shown a portion of a cylindrical steel gun body 24 of the perforating gun 20. The manner in which individual gun units are arranged in such gun bodies in spaced patterns is well known in the industry, and therefore only a portion of gun body 24, including one gun unit, is illustrated here. Gun body 24 contains a cylindrical, internally threaded barrel socket 26 having a horizontal axis. Socket 26 receives a cylindrical, steel, externally threaded gun barrel 28. Nine identical bores 30, having axes parallel to each other and to that of gun barrel 28, are arranged in a circular array and extend through barrel 28. A circular recess is formed in the end of barrel 28 to receive seal 32, which .covers the muzzle ends of all bores 30. Seal 32 keeps fluid out of the bores 30, and may be constructed of a soft metal such as brass.

A cylindrical firing charge 34 for the gun unit is contained in a generally cylindrical powder or cartridge receiving chamber 36 which comprises a coaxial, reduced diameter, inward extension of barrel socket 26. A coaxial, cylindrical opening 38 extends through charge 34. Circular shear disc 40, placed across the mouth of cartridge receiving chamber 36 flush with the inner wall of barrel socket 26, has an inwardly turned flange which ,sealingly engages the cylindrical wall of chamber 36. Re-

taining sleeve 42, which may be of fish paper or plastic, surrounds and retains firing charge 34 and has its forward end tucked inside inwardly curved flange shear disc 40. An unthreaded portion on the inner end of barrel 28 cooperates with an opposing unthreaded portion on the inner end of socket 26 to form a annular recess in which is placed an O-ring seal, which prevents well fluid which may seep inwardly between the threads of barrel 28 and gun body 24 from proceeding along the interface between the rear of barrel and the inner surface of socket 26 and getting into the bores 30 or firing charge 34.

The steelor steel-jacketed bullet 22 is located at the rear or breech end of each bore 30. These bullets 22 are of the conventional casingor formation-piercing configuration well known in the industry, having a conical or ogival shaped forward end and a transverse butt. While these bullets are of conventional shape, they have a diameter which is considerably smaller than that of the bullets or projectiles normally used in such a well piercing gun, as will be described in more detail below. A bullet retainer 44 holds each bullet 22 at the breech end of its corresponding bore 30, with its butt against shear disc 40. These bullet retainers 44 may be of any convenient material, such as paper or cardboard, which provides sulficient frictional engagement with the walls of bores 30 to retain bullets 22 in their desired position.

A contact pin igniter 46, which may conveniently be of the type described in Patent 2,649,736 to R. A. Phillips, is disposed at the rear of firing charge 34. If desired, other means for igniting the charge 34 may be used. It

"and form a filter.

tional bore.

comprises a generally cylindrical head 48, which contains an electrical resistance element and a combustible powder, placed in contact with the firing charge, and a reduced diameter stern portion 50 coaxial with an extension rearwardly of head 48. The forward half of igniter head 48 extends into cartridge-receiving chamber 36 through a circular aperture in retaining sleeve 48 and contacts firing charge 34. The rear half of igniter head 48 fits into a recess of generally cylindrical shape which forms a reduced diameter, coaxial, rearward extension of receiving chamber 36. Stem 50 extends rearwardly from head 48 and is insulated from gun body 24 by a sleeve of insulating material. The stem 50 has a threaded end which emerges into a cylindrical recess formed in the surface of gun body 24 at a point diametrically opposite to barrel socket 26. An electric wire from the electrical igniting or firing circuit is attached to a lug, which is placed upon threaded end of stem 50. The lug is insulated from steel gun body 24. A seal 54, placed across the mouth of the recess and sealingly attached to gun 'body 24, forms on its exterior a smooth continuation of the cylindrically-shaped gun body 24 and functions to keeps fluids from the electrical connections within the recess.

in operation, an electrical firing signal from an igniting or firing circuit, such as is well known in the industry, is applied through the lug and stem 50 to the resistance wire in the interior of igniter head 48. The combustible powder in igniter 46 is then fired and ignites in turn main firing charge 34. Shear disc 40 initially contains the gas created by burning charge 34 Within chamber 36, thus permitting the gas pressure within the chamber to rise to an optimum value before it is released to propel the bullets from the bores. The expanding gas compresses the overlapped retaining sleeve end and shear disc flange against the wall of receiving chamber 36, thus providing a gas-tight seal between the edges of shear disc 40 and the mouth of the cartridge receiving chamber. As the gas pressure reaches its optimum value, portions of disc 40 will be sheared off against the breech edges of bores 30 and the expanding gas will force the pieces of disc 40, along with bullets 22, out of bores 30. Seal 32 will be pierced by bullets 22 and start to follow the bullets 22 under the urge of residual gas blast which will move the seal 32 against the casing 14. Bullets 22 will pierce the well casing 14, the cement sheath 16, and travel into the formation 12 beyond, according to their design and the purposes of the gun. As mentioned, the seal 32 will follow the bullets 22 and will slam against the casing 14 with sufiicient force to flatten the protrusions around the perforations resulting from the passage of the bullets 22 through the casing 14 thereby eliminating burrs which could cause diificulty in subsequent running of close fitting tools.

The diameter of bores 30 is substantially less than the diameter of the single bore used in conventional wellperforating guns, in order that the corresponding penetrations in the casing 14 and cement sheath 16 will be small enough so that the sand will tend to bridge them While the size of the bores is not critical, a diameter of .125 has proven satisfactory for the nine-bore circular array shown and described in this embodiment. The centers of the bullets 22 have a ring diameter of M". The array of nine bullets 22 creates a pattern of holes in the casing v14 and a pattern of holes and cracks in the cement sheath 16. See FIG. 1. This permits a greater flow of oil than does a single hole of a small bore, and provides access to the formation over a larger area than does a single hole of a large or conven- Also, it has been found that the bullets 22 in the array diverge from each other after leaving the easing, see FIG. 1, and there is created in the sheath 16 a hole pattern more divergent, and, thus more desirable, since it provides access to the formation over a larger area, than that which would be normally expected from the bore pattern. It is believed that the diverging of the bullets 22 results from the fact that in penetrating the casing 14 the bullets cause the metal to How and when there is an array of bullets there is an interference set up due to change in density of material on the side of the bullet facing another bullet which causes the bullet to be diverted from its axis of flight. Once diverted, a bullet continues on its new diverted path. It has been further found that a much more satisfactory crack pattern, from the standpoint of large oil fiow and effective sand filtering, is set up in the cement well sheath than is the case with a single bullet.

As previously mentioned, it is essential that the cement sheath 16 be completely set and hard and that it have no additives which would cause softening or reduction in friability. It has been found that if the cement is green or if such additives are in the cement, the bullets will go through the cement without causing fracturing which tends to fill the perforations. In such case the penetrations, even though they are smaller than those customarily used in perforations, will be too large to establish a bridge for the sand. However, if neat cement is used and it completely fills the space between the casing and formation and is completely set and hardened, the crack pattern will be such that the fragmentations will tend to close the bullet perforations and the resulting fissures will permit bridging of the sand.

Also, since the diameter of the bullets 22 is small it has been found that very little of the cement sheath 16 is actually removed or reduced to powder. The effect of the fracturing of the cement sheath is to furnish particles of cement which will tend to close the bullet perforations and will move together in a random pattern so as to create a filter forming sufficient initial bridging points for the sand thereby precluding the sand from flowing into the casing where it can cause damage.

Accordingly, by utilizing a complete sheath of well set and hard friable cement and perforating the casing and cement sheath with an array of small diameter perforations, it has been found that the perforations will cause a crack pattern in the cement sheath which will result in the fragmentations tending to fill the perforations and establish bridging points for effective control of sand. Sand of a smaller grain size than the initial perforation can still be effectively held in check since the fragments form a random filter in the perforations which establish bridging points for the sand. Also, since the perforations diverge they form a larger effective opening for the flow of fluid than the original ring diameter of the perforations which establishes a larger fiow path for the fluid from the formation. Therefore, the practice of the method provides an economical and effective method of controlling sand in the completing of a well in an unconsolidated formation.

While the preferred form of the invention has been shown, it is understood that various changes may be made in its construction by those skilled in the art without departing from the scope of the invention as defined in the appended claims.

I claim:

1. The method of completing a well bore which extends into a zone of unconsolidated sand, which comprises:

lining the well bore with casing adjacent said unconsolidated sand zone,

forming a sheath of friable) cement between the wall of said well bore and said casing,

allowing the cement sheath to fully set and harden whereby said cement sheath is subject to fragmentation upon impact,

logging said bore to determine that there is a complete sheath of cement adjacent said zone, lowering a perforating gun into the casing to a position opposite the zone, the gun having an array of small diameter bullets,

firing said gun to form an array of perforations through said casing, said mement sheath and extending into said Zone, the perforations diverging from their original path as they pass through the cement sheath, the perforations causing the sheath to fracture where by fragmented portions of the sheath will tend to clo:e the perforations thereby forming a filter and preventing sand from entering the well bore.

2. The method of completing a well bore which extends into a zone of unconsolidated sand, which comprises:

lining the well bore with casing adjacent said zone,

forming a cement sheath of friable cement between the wall of said well bore and said casing,

allowing said cement sheath to fully set and harden,

whereby said cement sheath is subject to fragmentation upon impact,

lowering a perforating gun into the casing to a position opposite the zone, the gun having an array of small diameter bullets,

firing said gun to form an array of perforations through said casing, said cement sheath and extending into said zone, the perforations diverging from their original path as they pass through the cement sheath, the perforations causing the sheath to fracture whereby fragmented portions of the sheath will tend to close the perforations thereby forming a filter and preventing sand from entering the well bore.

3. The method of completing a well bore which extends into a zone of unconsolidated sand, which comprises:

lining the well bore with casing adjacent said zone,

forming a sheath of friable cement between the wall of said well bore and said casing,

allowing the cement sheath to fully set and harden whereby said cement sheath is subject to fragmentation upon impact,

logging said bore to determine that there is a complete sheath of cement adjacent said zone,

forming an array of perforations through said casing,

said cement sheath and extending into said zone, the perforations causing the sheath to fracture whereby fragmented portions of the sheath will tend to close the perforations thereby forming a filter and preventing sand from entering the well bore.

4. The method of completing a well bore which extends into a zone of unconsolidated sand, which comprises:

References Cited by the Examiner UNITED STATES PATENTS 12/1943 Turechek 16655.5 X 10/1948 Coggeshall 166-5 OTHER REFERENCES Uren: Petroleum Production Engineering, Development, fourth edition, 1956, McGraw-Hill Book Co. p. 705 relied on, TN870U7.

CHARLES E. OCONNELL, Primary Examiner.

T. A. ZALENSKI, S. I. NOVOSAD, Assistant Examiners. 

4. THE METHOD OF COMPLETING A WELL BORE WHICH EXTENDS INTO A ZONE OF UNCONSOLIDATED SAND, WHICH COMPRISES: LINING THE WELL BORE WITH CASING ADJACENT SAID ZONE, FORMING A SHEATH OF FRIABLE CEMENT BETWEEN THE WALL OF SAID WELL BORE AND SAID CASING, ALLOWING THE CEMENT SHEATH TO FULLY SET AND HARDEN WHEREBY SAID CEMENT SHEATH IS SUBJACENT TO FRAGMENTATION UPON IMPACT, FORMING AN ARRAY OF PERFORATIONS THROUGH SAID CASING, SAID CEMENT SHEATH AND EXTENDING INTO SAID ZONE, THE PERFORATIONS CAUSING THE SHEATH TO FRACTURE WHEREBY FRAGMENTED PORTIONS OF THE SHEATH WILL TEND TO CLOSE THE PERFORATIONS THEREBY FORMING A FILTER AND PREVENTING SAND FROM ENTERING THE WELL BORE. 